Liu, Zhu, Luo, Dong, Li , 2023
Experimental, mathematical model, and simulation of a dual-system self-centering energy dissipative brace equipped with SMA and variable friction device
In this study, a new self-centering energy dissipative (SCED) was developed and investigated on its seismic performance. The device is a dual system that comprises two main parts: shape memory alloy (SMA) system, and spring and wedge (SW) system. The proposed device was tested numerically and experimentally on three different fabricated specimens using cyclic loading for verification. The flag shaped load-displacement curves generated by the experiments validated theoretical predictions with their hysteretic behavior. The study concludes that using a wedge block system for energy dissipation and SMA system for self-centering exhibits satisfactory performance thus confirming an effective damper with high bearing capacity, high energy dissipation with minimal residual deformation.
System Concept
The proposed dual SCED device comprises two main systems: shape memory alloy (SMA) system and a spring-wedge (SW) system. The SMA system which is designed for energy dissipation includes a baffle, high-strength nut and an SMA screw. The SW system responsible for self-centering is made up of a middle cylinder, an outer cylinder, a baffle, spring and wedge blocks. The other component of the device is the push-pull rod which is connected to both systems. The design concept ensures that the SMA system only undergoes tension while the SW system only undergoes compression, regardless of the state of the brace. The SW system complements the SMA system by dissipating energy even under small strain while enhancing device stiffness and its capacity. In addition, the device is designed to expand its range of applications that demands different properties and performance, which can be satisfied by doing simple adjustment of key parameter values in the components, supported by theoretical and FE analysis from this study.
Experimental Study, Results and Discussion
Three different specimens – the SMA and spring combination (specimen 1), SW system (specimen 2) and the complete SCEB brace (specimen 3) – were fabricated and subjected to experimental testing. The test set up includes the SCED brace secured between a clamped hinge and a pin with a MTS machine grip head attached. The loading protocol for the test was at a frequency of 0.01 Hz of cyclic loading at 2.5 mm 5 mm, 7.5 mm, 10 mm, 15 mm, and 20 mm displacement amplitudes.
All three specimens generated flag-shaped satisfactory self-centering behavior on the load-displacement curves. However, a small superelastic range was observed due to degradation of SMA material and thus compromising the energy dissipative and self-centering capacity. It was also observed that SMA screws experienced shear failure due to bending tension. The study, therefore, suggested application of SMA wires or cables as a better alternative to avoid similar SMA failure. More studies are advised for SMA bending deformation since it can affect the shape of the load-displacement curve under small displacement.
The overall results such as self-centering capacity, energy dissipative capacity and bearing capacity were anticipated and confirmed with the theoretical calculations. The proposed model allows for a wider range of use through simple alterations in design parameters which is an advantage for application in different buildings.
Reference
Liu, T., Zhu, L., Luo, J., Dong, Y.-R., & Li, Z. (2023). Experimental, mathematical model, and simulation of a dual-system self-centering energy dissipative brace equipped with SMA and variable friction device. Journal of Constructional Steel Research, 211, 108219. https://doi.org/10.1016/j.jcsr.2023.108219